Glass or glass ceramic substrates provided with a decorative coating are known. In particular, at least partially transparent glass ceramic substrates such as those used for cooktops are provided with a bottom surface coating.
The decorative coating may be applied for functional reasons, for example to mark hobs. Also, a decorative coating may solely serve to create a special visual impression, for example to provide a hob in a specific color.
For applying decorative coatings, a variety of ways are known from practice.
For example, there exist decorative coatings applied by a sputtering process. Such sputtering processes are complex. Moreover, the options in terms of visual appearance are limited. In case of a partial coating, for example for marking hobs, complex masking steps have to be performed, and sputtered layers often exhibit an undesirably high conductivity, so that often they cannot be arranged behind capacitive switches.
Furthermore, silicone coatings are known. These have the advantage that they may easily be applied using a silicone paint, for example by screen printing, but usually exhibit non-optimal mechanical resistance and tend to discolor under high temperature loads.
Also known are glass flux-based layers, so-called enamel layers. A drawback of such pigmented glass flux-based layers is that they put the glass ceramic substrate under tension thus reducing its strength. This drawback can be alleviated by applying porous layers which however cause a matt appearance of the composite material so produced.
Furthermore, pigmented methyl group functionalized sol-gel coatings are known, which however are prone to cracking which is manifested as local lightening. The risk of cracking may again be reduced by applying porous sol-gel layers, which again is associated with a matt color appearance. In particular it is not possible to provide deep black glossy layers.
Lastly, it is known to apply luster paints. With luster paints, again, color choice is limited, and for producing deep black colors expensive noble metal based paints have to be used.